Coating



Feb. 24, 1953 P. GODLEY, 2ND ET AL COATING Filed April 6, 1950 m OE INVENTOR. Goo [2y 2 Phf/l o JC/ouq/v ATTORNEY Patented Feb. 24, 1953 were? COATING Philip Godley, 2nd, Lexington, and Philip J. Clough, Reading, Mass, assignors to National Research Corporation, corporation of Massachusetts Application April 6, 1950, Serial No. 154,306

7 Claims.

This invention relates to the formation of a metal-free stripe on a web of metal-coated, nonconducting sheet material, and is particularly useful in the manufacture of electrical condensers. This invention is particularly directed toimprovements in the process of removing metal from a metal-coated sheet as described in the ccpending application of Glenn L. Mellon et al., Serial No. 119,164, filed October 1, 1949.

In the above-identified application a plurality of electrodes are mounted so as to be moved successively into engagement with the metal-coated sheet material, each electrode, during the time of its engagement with the sheet, removing a preetermined portion of the metal coat by forming an arc therewith. As a result of this are the metal is vaporized, some of this metal condensing on the surface of the electrode. In practicing the above invention it has been found that, at

high speeds of operations, it is necessary to subject each electrode to a vigorous brushing by a wire brush. While this is a satisfactory method of removing the condensed metal from each electrode, the resultant brush wear has been found to constitute an appreciable portion of the total cost of manufacturing the coated paper. The brushes have been found to wear out quite rapidly with hard eiectrodes, and the electrodes have been rapidly worn when soft electrodes and hard brushes are used.

Accordingly, it is a principal object of the present invention to provid an improved process of the above type which minimizes brush wear and provides for ready cleaning of the electrodes even at the highest speeds of operation.

Another object of the invention is to provide an improved process and apparatus wherein the most advantageous materials may be used both for the electrode construction and the brush con struction, and the wear of both elements is kept to a minimum.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts, and the process involving the several steps and the rela. tion and th order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in Cambridge, Mass, 2.

2 connection with the accompanying wherein:

Fig. l is an isometric view illustrating in a diagrammatic fashion one preferred embodiment of the present invention;

Fig. 2 is an enlarged, diagrammatic, elevation view of one of the electrodes of the apparatus of Fig. l; and

Fig. 3 is an enlarged, diagrammatic end view of the electrode illustrated in Fig. 2.

in the present invention, which will be particularly described with reference to removal of a predetermined coating of zinc from a zinc-coated condenser paper, it has been discovered that greatly improved results can be achieved in removing condensed zinc from the electrodes by so treating the electrodes that adhesion of the condensed zinc to the electrode is greatly diminished. It has been found that there are two principal ways of achieving this decrease in adhesion between the condensed zinc and the electrode. In a preferred form of the invention both of these systems are used jointly. The first method of decreasing the adhesion between the zinc and the metal of the electrode comprises the use of at least a surface stratum on the electrode of a material which has a very low solid solubilit in zinc. Due to this low solid solubility in the zinc, the zinc does not readily wet the electrode, and therefore does not form a very good bond with the electrode. The second method comprises the use of a thin film of a liquid on the electrode, this film of liquid acting, where it exists, to prevent adhesion between the condensed zinc and the material of the electrode. It has been found that this liquid should preferably be a lubricant and one which is not completely vaporized by the hot zinc condensing thereon.

In a preferred form of the invention it has been found that chromium has a very low solid solubility in zinc. Consequently, each electrode is preferably provided with a chromium plate. The liquid, which is additionally employed in a preferred form of the invention, preferably comprises a lubricating oil, such as a hydrocarbon. The viscosity of the lubricating oil is preferably low so that it forms a very thin film. The thinness of the film is quite important, particularly when low voltages are to be employed for the meta1-removing arc. The reason for this requirement is that a thick film of oil can actas a dielectric which prevents striking the arc at low voltages. At high voltages this is not particularly critical. However, the high voltages are not drawings preferred since they are apt to burn the delicate condenser paper.

Referring now to the various figures in the drawing, there is shown. one representative Eu." bodiment of the invention. In these figures like numerals refer to like elements, and the web of metal-coated sheet material is indicated at Ii] as being fed from one roll l2 thereof to a windup roll I4 thereof, these two rolls being supported on suitable axles I5 and I8 respectively. For guiding the web in its path of travel, there are provided. guide rolls 20, 2| and 22, it being seen that guide rolls 2B and 22 engage the metal coated surface 24 of the web, while the roll 2| engages the upper surface 25 of the web. Positioned between the two guide rolls 2| and 22 is the plurality of electrodes 26. The outer end of each electrode 26 has a width substantially equal to the desired width for the metal-free strip iiila, these electrodes being preferably mounted on a rotary support, such as a wheel 28. Two electrode Wheels 26, 28 are shown as being mounted on a common shaft 29. The wheel 28 is preferably formed of an insulating material and carries the electrodes 25 uniformly arcuately spaced around the circumference thereof. Near the center of wheel 28 the various electrodes 26 are exposed so as to provide a commutator which is engaged by a commutator brush. for successively energizing the various electrodes. In a preferred arrangement, the COll'l-- mutator brush 30 has an arcuate length slightly greater than the arcuate spacing of the electrodes, so that two of the electrodes may be simultaneously energized.

As seen best in Fig. 2, each of the electrodes 26 preferably includes a knife edge for concentrating the are created, as described hereinafter, between the electrode 26 and the metal coating 24. This knife edge is slightly rounded, as at 33, to prevent tearing of the web In as this web moves in a direction opposite to the movement of the electrode.

As can be seen best from Fig. l, the electrode wheel 26, 28 is so positioned with respect to the straight line path between rolls 2| and 22 that the electrodes 26 deviate the web It] only slightly (about 1-2) from this straight line path. For applying a potential difference between one of the electrodes 26 and the metal coating 24, there is provided a source of electrical energy, preferably a low impedance source such as a battery 36, the positive side of the battery being preferably grounded, and the negative side of the battery being preferably connected to the commutator brush 3!]. For completing the electrical circuit to the metal surface 24, the rolls 20 and 22 are also preferably grounded. This arrangement is particularly convenient since it allows most of the elements of the apparatus to be at ground potential while the electrodes and the commutator brush 30 are at a potential of about minus 20 volts.

The means for removing metal deposited on the electrode 26, as the result of arc vaporization of the metal, preferably comprises a brush 38 driven by a motor 40, the brush being preferably positioned near the bottom part of the path of travel of the electrodes. This brush 38 is preferably mounted so that its axis is at to the plane of rotation of the electrodes.

The means for advancing the web through the apparatus preferably comprises a roll 42, driven by motor 44, roll 42 engaging the outer surface of the web roll l4. The axle i8, supporting roll '4 I4, is preferably provided with a floating mounting so as to permit axle 18 to move away from the axis of roll 42 as the radius of web roll l4 increases. The electrode wheel 28 is also preferably driven, through a suitable connection, by means of motor 44.

Positioned adjacent the periphery of the path followed by the electrodes 25 is a means for applying the liquid to each electrode prior to its engagement with the metal coating 24 on the subtrate 25. In the preferred form shown, this means comprises a wick 46 which is kept saturated with the liquid 48 which may be conveniently stored in a reservoir 50. This wick 46 is shown as being positioned so as to apply the thin film of oil to each electrode after the electrode has passed the brush. It has been found to be equally practicable to apply the oil to the electrode prior to brushing. In this case the zinc on the electrode seems to absorb the oil and the brush also picks up some of the oil, there being sufficient oil left on the electrode after brushing to form the desired thin film.

In a preferred embodiment of the invention, the metal-coated subtrate comprises condenser paper having a vacuum-deposition coating of zinc of the order of micron thick. Such a thin coating is readily vaporized by the low volt age are employed. The individual electrodes 26 are preferably formed of steel which has been ground so as to have a slight transverse curvature on the end thereof. This curvature is shown in Fig. 3 and is preferably made to have a radius of about 1.5 inches when the electrode has a width of approximately 0.25 inch. The electrodes 25, after shaping to the approximate dimensions shown, are then preferably chromium plated, as indicated at 52. The liquid 48 preferably com prises a lubricant and more particularly a light hydrocarbon having a viscosity less than that of SAE 30. One suitable oil is that sold by the Dumore Company under the trade name Dumore and the designation No. 0 high-speed ballbearing oil. The wick 46 preferably comprises a piece of felt.

In practicing the invention described above, roll 52 of the web of metal-coated condenser paper is suitably mounted in the apparatus, and the web is fed past the rolls 26 and 2i, over the electrode wheel 26, 28, and over roll 22. The end of the web is attached to the floating axle H3. The oil reservoir 50 is filled and the device is put into operation by starting motor 44 to rotate the web roll M. The web, as shown, travels from right to left While the electrode wheel 26, 23 rotates in a clockwise direction. Thus the electrodes, while in engagement with the web, are traveling in an opposite direction to the movement of the web. The wheel 28 is preferably rotated at such a speed that each electrode is in contact with approximately nine inches to one foot of web length for each rotation of the wheel 28. As the wheel 28 rotates, the electrodes are successively brought into contact with the web, each of these electrodes having been wetted with the oil 48 prior to engagement with the metal coating. As the first electrode contacts the metal coating 24, which is at ground potential, an arc is struck between the metal surface and the electrode. This are serves to vaporize the thin metal coating which condenses on the electrode around the tip 33 and along the base of the electrode.

Fig. 2, the oil film 48 is evaporated from the tip This condensed metal is shown in 2 at 24c. As can be seen from.

33 due to the high heat in the arc. Consequently, at the tip 33 there is no protecting film of oil between the condensed metal and the surface of the electrode. However, the coating 52 is not affected by the heat of the arc and remains in tact on the tip 33. When about nine inches to one foot of coated surface has passed the first electrode, this electrode has meanwhile rotated so that the base thereof is no longer in contact with the commutator brush 30. Shortly thereafter, the first electrode moves out of engagement with the web. Meanwhile, the next succeeding electrode has been rotated into contact with the web and its base has been contacted b the commutator brush 30 so that it is maintained at the minus 20 volts potential. When this next electrode first contacts the web, there is no arcing since it contacts only the metal-free paper base 25 which is a nonconductor. When the preceding electrode is de-energized, the arc is extinguished and the metal coat advances to the succeeding electrode. When the metal coat touches this succeeding electrode, the arc is struck and the metal stripe is removed from the advancing web as previously described. As each electrode, with its coat 24a of condensed metal, rotates around to the position of the wire brush 3B, the metal coat is easily removed therefrom, since practically all points on the coating 24a have the oil film 48 between the condensed metal and the chromium plate 52 of the electrode. A very light brushing of this portion of the coating 24a serves to remove it. The condensed metal on the tip 33 of the electrode, while being more strongly bonded, can be readily removed, since it has no structural unity with the remainder of the coating 24a and moderate brush pressure on the tip 33 has been found to completely remove that portion of the coat 2464 which is on the tip 33.

When utilizing a chromium plated electrode and the oil film, it has been found that a brush speed of approximately 1500 R. P. M. and a brush contact with the electrode of approximately inch are completely adequate to remove all traces of condensed zinc from the vicinity of the tip of the electrode. Consequently, when the electrode engages the next portion of the metalcoated web to be striped, a completely uniform are is maintained and no islands of metal remain in the striped portion. This is true even at the very high speeds of operation, such as speeds of web travel of over 200 ft. per minute.

The transverse curvature of the electrode illustrated in Fig. 3 has been found to be of considerable advantage, it preventing tearing of the web and assuring positive contact between the surface of the web and the electrode since the curvature of the electrode matches the normal curvature of the sheet due to the movement of the sheet from its normal plane.

For simplicity of illustration, the electrical connections to only one electrode wheel 25, 23 have been shown. It is preferred to have each of the electrode wheels 26, 28, which mounted on the common rotating shaft 29, arranged so that corresponding electrodes are equally arcuately spaced around shaft 29, each of the corresponding electrodes being electrically connected to a corresponding contact extending between the various electrode wheels. This arrangement has the advantage that a single commutator brush 30 may be employed to energize the cor responding electrodes in the various electrode wheels.

Since certain changes may be made in the above apparatus and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompany ing drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. The process of forming a metal-free stripe on a web of metal-coated, nonconducting sheet material which comprises advancing the web, providing a plurality of electrodes adjacent said advancing web, applying to each said electrode a thin film of a liquid, moving said wetted electrodes successively into contact with the metal coating on the advancing web, applying a potential difference between said metal coating and each electrode during a portion of the time each said electrode is in contact with the web to create a metal-evaporating are between said electrode and said coating, removing said potential difference, thereafter moving said electrode out of contact with said web, and removing from said electrode metal vaporized by said are and deposited on said electrode, said liquid comprising a low viscosity oil, said oil preventing the formation of a strong bond between said condensed metal and said electrode, said film of oil being sufficiently thin so as not to prevent formation of said are at a relatively low voltage.

2. The process of forming a metal-free stripe on a web of metal-coated, nonconducting sheet material which comprises advancing the web, providing a plurality of electrodes adjacent said advancing web, each said electrode comprising a surface stratum having a low solid solubility in the metal of said metal coating, applying to each said electrode a thin film of a liquid, moving said wetted electrodes successively into contact with the metal coating on the advancing web, applying a potential difference between said metal coating and each electrode during a portion of the time each said electrode is in contact with the web to create a metal-evaporating arc between said electrode and said coating, removing said potential difference, thereafter moving said electrode out of contact with said web, and removing from said electrode metal vaporized by said are and deposited on said electrode, said liquid comprising a low viscosity oil, said oil preventing the formation of 'a strong bond between said condensed metal and said electrode, said film of oil being sufficiently thin so as not to prevent formation of said are at a relatively low voltage.

3. The process of claim 1 wherein said liquid comprises a hydrocarbon lubricating oil having a viscosity less than that of SAE 30 and said metal coating comprises zinc.

4. The process of claim 2 wherein said surface stratum on said electrode comprises chromium and said metal coating comprises zinc.

5. The process of claim 2 wherein said are voltage is on the order of about 20 volts.

6. Apparatus for forming a zinc-free stripe on a web of zinmcoated, nonconducting sheet material by removing a band of said zinc coating, said apparatus comprising means for advancing the web, an electrical contact positioned to engage the zinc face of the web. a plurality of electrodes successively positionable adjacent said zinc coating, each said electrode having a width, extending across the advancing web, which is on the order of the thickness desired for the zinc-free stripe, each said electrode comprising a surface stratum of chromium, means for movhas said electrodes successively into and out of engagement with said web, means for maintain ing a sufiicient potential difference between one oi said electrodes in contact with the web and the zinc face of the web to create an arc be tween said zinc coating and said electrode, said last-named means being arranged to remove said potential difference prior to movement of said electrode out of engagement with said web, means for applying a thin film of a low viscosity oil to each electrode prior to contact of said zinc coating by said electrode, and means for removing from each said electrode zinc evaporated by the are which condenses on the electrode.

'7. Apparatus for forming a metal-free stripe on a web of metal-coated, nonconducting sheet material by removing a band of said metal coating, said apparatus comprising means for advancing the web, an electrical contact positioned to engage the metal face of the web, a plurality of electrodes successively positionable adjacent said metal coating, each said electrode having a width, extending across the advancing web, which is on the order of the thickness desired for the metal-free stripe, each said electrode comprising a surface stratum having a low solid solubility in the metal of said metal coating, means for moving said electrodes successively into and out of engagement with said web, means for maintaining a sufiicient potential difference between one of said electrodes in contact with the web and the metal face of the web to create an arc between said metal coating and said electrode, said last-named means being arranged to remove said potential difference prior to movement of said electrode out of engagement with said Web, an oil reservoir and a wick positioned in the path of travel of said electrode for applying a thin film of a low viscosity oil to each electrode prior to contact of said metal coating by said electrode, and means for removing from each said electrode metal evaporated by the are which condenses on the electrode.

PHILIP GODLEY, 2m.

PHILIP J. CLOUGH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 837,296 Fulton et a1. Dec. 4, 1906 1,267,400 Gravell May 28, 1918 1,862,392 Afileck et al. June '7, 1932 1,909,079 Steerup May 16, 1933 2,141,869 Konig Dec. 27, 1938 2,435,441 Grouse Feb, 3, 1948 2,569,414 Godley, 2nd., et al. Sept. 25, 1951 FOREIGN PATENTS Number Country Date 352,911 Great Britain Jan, 9, 1930 

6. APPARATUS FOR FORMING A ZINC-FREE STRIPE ON A WEB OF ZINC-COATED, NONCONDUCTING SHEET MATERIAL BY REMOVING A BAND OF SAID ZINC COATING, SAID APPARATUS COMPRISING MEANS FOR ADVANCING THE WEB, AN ELECTRICAL CONTACT POSITIONED TO ENGAGE THE ZINC FACE OF THE WEB, A PLURALITY OF ELECTRODES SUCCESSIVELY POSITIONABLE ADJACENT SAID ZINC COATING, EACH SAID ELECTRODE HAVING A WIDTH, EXTENDING ACROSS THE ADVANCING WEB, WHICH IS ON THE ORDER OF THE THICKNESS DESIRED FOR THE ZINC-FREE STRIPE, EACH SAID ELECTORDE COMPRISING A SURFACE STRATUM OF CHROMIUM, MEANS FOR MOVING SAID ELECTRODES SUCCESSIVELY INTO AND OUT OF ENGAGEMENT WITH SAID WEB, MEANS FOR MAINTAINING A SUFFICIENT POTENTIAL DIFFERENCE BETWEEN ONE OF SAID ELECTRODES IN CONTACT WITH THE WEB AND THE ZINC FACE OF THE WEB TO CREATE AN ARC BETWEEN SAID ZINC COATING AND SAID ELECTRODE, SAID 